1. Field of the Invention
The present invention relates to a projection apparatus that has a plurality of light sources and that is provided with a function enabling it to switch the in-use light source at light-source replacement time, to extend the period the apparatus is useable, and relates to projection apparatus technology for yielding predetermined light source service life in a use mode in which images are projected horizontally as well as in a use mode in which images are projected vertically.
2. Description of the Background Art
In general, projection apparatuses referred to as projectors mainly use, as a light source, a discharge lamp such as a high pressure mercury lamp, and converge light generated by the light source, in one direction by a reflector, to emit the light. The light source such as a discharge lamp provides a high brightness by using a small light-emitting element. However, the light source has the following problems, since a plasma state occurs by an electric discharge between electrodes, causing a high temperature close to 1000 degrees and a high pressure close to 200 atm.                The service life indicating a brightness half life is 1500 to 3000 hours and is not sufficient.        When the temperature distribution of a bulb becomes nonuniform, the bulb cannot resist the internal pressure and there is the possibility that degradation in brightness or rupture will occur.        In order to obtain desired performance, the inclination of an axis connecting discharge electrodes of the light source (hereinafter, referred to as a discharge electrode axis), in other words, a center axis of light converged by the reflector—which center axis is coincident with the discharge electrode axis (hereinafter, referred to as a reflector center axis)—needs to be equal to or less than about 10 degrees relative to a direction perpendicular to the direction of gravity.        
Due to the above reasons, in projection apparatuses, the optical axis of a projection lens for projecting an image on a screen and the discharge electrode axis or the reflector center axis are orthogonal to each other, in order to allow projection to be performed even when the projection apparatuses are installed in an inclined manner.
A first object of the present invention is to lengthen the period during which even an apparatus using a discharge lamp having a short service life is useable. With regard to the first object, a technique in which a plurality of light sources are provided and the period the apparatus is useable is extended by switching and continuously using the light sources is proposed in Patent Document 1 (Japanese Laid-Open Patent Publication No. 2005-221762). In an apparatus structure (FIG. 9) proposed in Patent Document 1, two light source sections each including a light source and a reflector are provided such that the reflector center axes 161 thereof are orthogonal to the optical axis 160 of a projection lens. Then, the in-use light source is switched by rotating a mirror 162.
A second object of the present invention is to obtain a predetermined light source service life in both of use modes of horizontal projection and vertical projection of images. In general, projectors are designed such that a horizontally projected image is obtained. In recent years, there is a demand to use a vertically projected image for the purposes of advertisement. However, conventional projection apparatuses assume only a use mode in which images are projected horizontally, and it is difficult to rotate the apparatuses by 90 degrees to perform vertical projection of an image. In this case, it suffices to manufacture an apparatus dedicated for vertical projection of an image (see Japanese Laid-Open Patent Publication No. 2006-295584 (Patent Document 2)), but this single apparatus cannot solve the object to enable both of the use modes of horizontal projection and vertical projection.
The above apparatus structure proposed in Patent Document 1 can achieve the first object but cannot achieve the second object at the same time. In other words, when the reflector center axes 161 of all the light sources are orthogonal to the optical axis 160 of the projection lens as in the apparatus structure in FIG. 9, there is no problem if the apparatus is installed so as to extend in a horizontal direction that is perpendicular to the direction of gravity, as shown in FIG. 9. However, if the apparatus is rotated by 90 degrees and installed vertically, the reflector center axes 161 of the light sources are coincident with the direction of gravity. Thus, the above problem arises that the temperature distribution of the bulb becomes nonuniform, and the apparatus cannot be operated.
Further, Patent Document 2 has a description concerning an apparatus dedicated for vertical projection of an image but does not have any description concerning a light source section for implementing horizontal projection of an image.